Resonant burner



Oct 4, 1966 HUBER ETAL 3,276,505

RESONANT BURNER Filed Feb. 14, 1964 2 sheets-sheet 2 WVM/70H5 LUDwl HUBER FRA/v2 Hm BY MM50/wm frm,

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United States Patent C) 7 claims. (ci. 15s- 4) This invention relates in general to combustion devices, and in particular to a new and useful resonant pulse jet combustion device with a tubular member forming a combustion chamber anda resonant exhaust pipe and in which fuel is admitted into the combustion chamber in an axial direction into an ante-chamber portion having diverging side walls constructed in the manner of a diffuser.

The present invention relates particularly to combustion devices of a type in which a combustion cha-mber is formed as a portion of or leads directly into an exhaust pipe, which is of a length to cause the periodic drawing in of a combustible mixture into the chamber and a detonation thereof at the natural lfrequency of the device. Resonant burners or so-called resonant pulse jet combustion devices consist essentially of a combustion chamber having connected thereto an unrestricted or valveless exhaust pipe or resonant tube. Pulsating detonations or fuel combustions take place in the combustion chamber and the frequency of such detonations depends on the inherent or natural frequency of the system comprising the combustion chamber and the exhaust pipe. The combustion cham'ber pressure fluctuates Vperiodically at the natural frequency of the device between super at-mospheric and sub-atmospheric values. The combustion chamber is connected to means for supplying a fuel and air mixture and for separately supplying additional combustion air which is drawn in into the combustion chamber when the pressure in the combustion chamber is sub-atmospheric.

With pulse jet combustion devices of the type mentioned above, a number of measures have to be considered in order to properly utilize the natural frequency of the system, and in order to properly utilize the fuel and insure that it is burned properly. One difficulty in the operation of such a device is the formation of carbon from the fuel particles, or the coking of the fuel, which is particularly acute, for example, with diesel oil or lead-containing gasoline and which usually takes place at the walls of the system.

In accordance with the prior art, it has been known to inject the fuel into the combustion chamber in the form of a spray. In so doing, `droplets of smaller and larger size are formed. The smaller droplets burn up before their core reaches the coking temperatures. However, the larger droplets do not burn well and they tend to coke to an extent such that only pure carbon remains which will no longer burn at the temperatures maintained within the combustion chamber. When the droplets impinge on the combustion chamber wall, it frequently happens that the wall which has previously been heated by combustion, causes the coking of the -liquid fuel which results in the formation of `a thick carbon layer. There is also the possibility that the wall portions which are heated and which are struck by the injected fuel are not sufficiently hot to cause coking. It should also be considered that the operating conditions during the initial starting stages of the burner are generally considera-'bly different than the conditions after some time of operation. Evidently, a reliable resonant burner should operate reliably and economically during all phases of operation.

In accordance with the invention, there is provided a resonant burner which overcomes the disadvantages of the prior art mentioned above.

3,276,505 Patented Oct.. 4, 1966 "ice In a preferred arrangement, the combustion chamber and exhaust pipe are formed as an elongated tube with the inner portion formed as an ante-chamber in the manner of a diffuser. A fuel and air mixture is admitted directly into the end of the combustion chamber at the location of the diffuser and at the smaller diameter portion thereof. At this location, the walls of the diffuser or antechamber portion diverge outwardly. The construction is such that fuel which is directed axially into the elongated combustion chamber creates an axial fuel jet, which is composed of finer and coarser particles. When this jet can move without encountering any obsta-cles, it may cause -an annular turbulence in the surrounding antechamber portion, which turbulence only insignificantly iniluences the path of the larger droplets while the ner droplets which first ilow along the axis of the ante-chamber are brought to the vicinity of the combustion chamber wall at which point the formed mixture can be readily ignited. It should be appreciated that while the lantecharn-ber portion of the combustion chamber' is termed a diffuser, the flow conditions at such location are not the same as diffuser llow.

A principal feature of the invention is the manner in which the fuel is supplied to the combustion chamber in an axial direction. The fuel supply system includes an atomizer which terminates either within the ante-chamber portion or adjacent the end thereof. An axial conductor channel of the atomizer opens on its one end directly into the combustion chamber, and is connected at its opposite end to a fuel collecting chamber at a location above the fuel level. The conduit is provided for supplying either starting combustion air or fuel gas from the top of the fuel tank or container. A separate fuel conduit extends from the fuel chamber at a location below the fuel level to an annular passage around the central conduit. When the pressure in the combustion chamber is sub-atmospheric, the gas which moves through the central passage draws the fuel through the annular passage and an atomization thereof takes place directly within the combustion chamber in the ante-chamber portion thereof.

The device of the invention is started by supplying air under pressure to the atomizer, preferably through the fuel chamber at a location above the fuel level so that the incoming air will scavenge the top of the fuel chamber during operation and take along any atomized or vaporized fuel particles.

The fuel which is supplied to the combustion chamber from the atomizer is supplied in a radial manner, radially into the gas stream which exits from the central bore, directly into the combustion chamber. The fuel particles are broken up *by the to and Vfro oscillating gas ow in the central bore produced by the cyclical detonations and pressure variations and they are carried along by the gas llcw in the form of droplets. Experience has shown that this manner of axial supply of fuel ensures a rapid and reliable starting up of the burner even if diesel oil is used, and no coking takes place.

In respect to the avoidance of coking, it should be noted that the droplets of fuel preferably become positioned at the marginal zone of the axial jet and they extend into the combustion space. During operation, however, and due to the back and forth movement of the combustion air or gas, these droplets are prevented from leaving the diffuser space and therefore are deposited within this space. The diffuser section is, of course, heated during operation, however, it is possible to limit the heating of this space to such an extent that coking of the fuel is prevented, and in contrast thereto, the fuel is rapidly evaporated by the moistened wall and thus is readily ignited.

In accordance with a feature of the invention, the atomizer comprises two axially spaced plates having aligned central openings or apertures. The plates are advantageously carried at the end of the inner or central tube for conducting air or gas and at the end of the outer conduit which forms a surrounding conduit for conducting liquid fuel from the fuel chamber. Fuel is supplied from the conduit surrounding the central gas conduit to the space between the tw-o plates and the ow of fuel at such location is radially inwardly toward the central apertures. Preferably, the edge of the discharge plate which faces the combustion space is formed as a sharp edge in order to obtain efficient breaking up of the fuel droplets. It is also advantageous that this discharge plate form that portion of the fuel supply which is situated to extend the furthest into the combustion chamber in the direction of ow so that after the exit or discharge of the fuel from the nozzle, no larger drops can thereafter form. In doing this, the nozzle end may project somewhat into the combustion chamber space or it may even be arranged flush with the end of the combustion chamber. It is also possible that this nozzle end be somewhat retracted or offset, for example, it may be positioned in a smaller pipe-like space which is arranged in front of the diffuser. This space may also be arranged coaxial in respect to the diffuser portion of the combustion chamber.

The inventive construction preferably includes an arrangement in which the main combustion air supply is through a Separate conduit Which connects into the diffuser or ante-chamber portion of lthe combustion chamber, at a location further toward the enlarged main combustion chamber portion than the atomizer. Particularly beneficial effects have been obtained in a construction in which the combustion air supply is directed tangentially into the diffuser portion of the combustion chamber.

Accordingly, it is an object of this invention to provide an improved pulse jet resonating device.

A further object of the invention is to provide a pulse jet resonating device in which the fuel is directed into an ante-chamber or a diffuser portion of the combustion chamber formed with walls which diverge outwardly from the fuel injection location, and in which the fuel is directed substantially axially.

A further object of the invention is to provide a pulse jet resonating device which includes an elongated combustion chamber `of resonant characteristics having a diffuser portion at its closed end with an atomizer positioned at the location of the smallest diameter, which is arranged to direct fuel axially into the combustion chamber, and wherein the atomizer includes a central conduit for the back and forth ow of a gas and an annular surrounding conduit for conducting fuel into the gas stream as it is directed into the combustion chamber.

A further obje-ct of the invention is to provide an atomizer for a pulse jet combustion device, which cornprises a central conduit with a passage of gas backwardly and forwardly into the combustion chamber adapted to be arranged to extend axially outwardly from an end of the combustion chamber, and further including an annular conduit for the supplying of fuel, the conduits being closed at each end by plate members having .apertures such that the fuel ow is directed radially into the central gas stream of the central conduit 'between the plate members for discharge through the apertures into the combustion chamber.

A further object of the invention is to provide a pulse jet comb-ustion device which is simple in design, rugged in construction and economical to manufacture.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding `of the invention, its operating advantages and specific objects attained by its use, reference should be had `to the accompanying drawing and descriptive matter in which there is illustrated .and described a preferred embodiment of the invention.

In the drawings:

FIG. 1 is a longitudinal section view of a pulse jet combustion device constructed in accordance with the invention,

FIG. 2 is a cross section al-ong line IIII of FIG. l, while FIG. 3 is a `cross section along line III-III of FIG. l.

Referring to the drawing, in particular, the invention embodied therein comprises a combustion chamber geuerally designated 50, which in accordance with the invention, inclu-des Va substantially cylindrical elongated combustion chamber portion 1 and a diffuser portion or antechamber portion 2 on one end, The opposite end of combustion chamber portion is connected to a resonance exhaust pipe or tube 1. A feature of the construction is that the ante-chamber portion 2 is provided with external cooling fins or ribs 3 for maintaining this portion at a temperature which especially in the narrower portion is below the coking temperature of the fuel. A principal supply of combustion air for operating the device is obtained through a conduit 4 which connects through an opening S tangentially into the antechamber portion 2 intermediate the length thereof. While only one such tube 4 is indicated for clarity of illustration purposes, it should be appreciated that a plurality of such tubes may be provided.

In accordance with a further feature of the invention, the end of the combustion chamber having the smallest diameter, that is the smaller diameter end of the diffuser portion 2, is provided with an atomizer generally designated 52 which is arranged to discharge either starting air or a carrier gas and fuel axially into the interior of the diffuser section 2.

The atomizer 52 comprises an outer tubular housing 54 having anges at each end for connection to the end of the diffuser section 2 and to a flanged extension 56 of a fuel tank or container 17, respectively. A relatively small diameter and a relatively large diameter pipe 7 and 8 are arranged coaxially within the housing 54 and each terminates on the combustion chamber side with an apertured plate or diaphragm plate 9 and 10, respectively having apertures 9a and lila, respectively. The aperture or opening 10a of the discharge plate 10 is advantageously made somewhat smaller than the opening 9a of the other plate 9. An annular space 11 defined between the pipes 7 and 8 provides a fuel flow channel which connects to an annular chamber 12. An outer annular chamber 14 connects to the annular chamber 12 by a plurality of bores 13 and is connected directly through a line 15 to the fuel container 17 at a location below the liquid fuel level. The line 15 may be provided with an adjustable or exchangeable throttle or nozzle portion 16. Thus, fuel can ow from the container 17 through the conduit 15 and into the annular space 11 at the combustion end of which the fuel ows radially inwardly toward the apertures of the plates 9 and 10. The radial fuel flow is at the location 18 indicated in the drawing.

The pipes 7 and 8 include end flanges 19 and 20 which `are sealed by means of a nut 21 and packing 22 and 23. In order to support this system, a jacket 24 containing the bores 13 is provided, which may comprise a portion of the inner pipe 7. A tubular pipe 25 connects the center of the inner tube 7, i.e., the cylindrical space 26, to the interior of the fuel container 17 at a location above the level of the fuel. A supply pipe 27 for supplying a pressurized gas such as air emanating from a `blower fan or manually actuated pump, or the like, connects to the upper portion of the liquid container 17. A fuel supply tube 28 also connects to the upper portion of the fuel container 17 and the admission of fuel is regulated in accordance with the position of a needle valve 29, which is carried by a float 30. When the level of the fuel within the container 17 is high enough, the needle valve 29 closes off the conduit 28 so that no further fuel is supplied to the interior of the chamber 17.

n the embodiment indicated in the drawing, the inner and outer pipes 7 and 8 are of a length so that they project slightly into the diffuser section 2. However, these parts may be easily removed by unscrewing the member 21 which is threaded into housing 54. When this is done, conduits 7 and 8 of a smaller length may be employed in which case the inner end of the outer conduit may be ush with the end of the diffuser section 2. In some instances, in fact, it is preferable to have the discharge apertures of the plates 9 and 10` located in a recess formed beyond the end of the diffuser section 2, that is retracted within the housing 54.

The device operates in the following manner; To start ,the device air is blown through the pipe 27, such as with the aid of a manually operated pump or by the use of an air pressure feed device, into that portion of the fuel collecting chamber above the liquid fuel level. The tank 27 is automatically closed off such as by the manually operated pump or by a check valve (not shown) when one stops pumping such as disclosed in U.S. Patent No. 2,959,214. When the pressure supplied to chamber 17 is higher than the pressure in the combustion chamber 1, a fuel laden stream will move through opening 25 and passage 26 through the openings 9a and 10a into antechamber 2. As soon as the pressure in chamber 17 becomes smaller than that in the combustion chamber, the gas flow will pulse in an opposite direction. This air carries along the fuel vapors which are contained in the fuel collecting chamber above the fuel level and the air with the fuel entrained enters through the passage 25 into the space 26 and is discharged through the openings 9a and 10a and the plates 9 and 10 directly into the ante-chamber or diffuser section 2 of the combustion chamber 5ft In this manner, this air creates between the plates 9 and 10 in the radially situated space 18 a vacuum or sub-atmospheric pressure which vacuum or sub-atmospheric pressure causes suction of the fuel in the manner previously described. In addition, the fuel is positively urged into the space 18 by the pressure which acts downwardly on the fuel which is in the container 17.

The air flow through the central tube 7 causes the atomization of the Ifuel and creates within the ante-chamber portion 2 an ignitable mixture which may be ignited by a suitable igniting device 2 which, for example7 may comprise an intermittently operable electrical spark plug or a glow plug 2. The device will also operate with a hot red wire or the like.

Flame from the combustion of the mixture which includes the combustion air admitted through the conduit 4 heats the ante-chamber 2 and the combustion chamber 1 until sufficient fuel for a detonation has been burned. This detonation creates first a super-atmospheric pressure in the spaces defined by the combustion chamber 1 and the ante-chamber 2 and, consequently, combustion gases flow through the openings 9a and 10a in the plates 9 and 10 as well as through the outer open end of the antechamber 2, the cylindrical combustion chamber 1 and the exhaust pipe 1. The combustion gases also flow through the space 26 and the conduit 25 into the fuel chamber 17 above the fuel level. During the detonation phase of the cycle, return flow of gases from the ante-chamber 2 will flow through the openings 9a and 10a of the plates 9 and 10 because the pressure in the combustion chamber 1 will exceed that of the tank 17. This flow in a reverse direction causes a continuous inow of liquid fuel through the line 1S and into the annular space 11 the same as when flow is in an opposite direction. The liquid fuel is taken along by the gases through opening 10a and it is atomized or torn apart into droplets and vaporized as it is moved. As the fuel becomes atomized, it flows along as part of the fuel enriched gas flow.

Detonation or explosion is followed by a sub-atmospheric pressure phase which is created and a new charge of the fuel enriched gases is brought in until atmospheric conditions are again approached. The conduit 4 is provided with a combustion air inlet valve 4a which opens permitting in ow of combustion air only when the pressure within the combustion chamber is sub-atmospheric, but closes to prevent back ow of combustion air or gases through the conduit 4 when super-atmospheric conditions are prevailing. The inflow of the combustion air in a tangential manner causes the further breaking up of the fuel and air mixture which exits through the openings in the plates 9 and 10 into the combustion chamber and insures that the fuel is broken up into fine droplets. The same cycle is repeated over and over. However, additional air supply through the line 27 is not necessary after the initial start-up stage. The operation terminates when the fuel valve, indicated at 31, is closed.

During the ignition rhythm, which is set up during operation, there is formed an annular turbulence about the axis of the air-gas-jet which enters into the anteehamber 2 from the openings in the plates 9` and 10 :and which is charged with liquid droplets. This annular turbulence bears against the wall of the ante-chamber 2. Since the larger droplets are not affected by this turbulence and thus continue to move, that portion of the turbulence which flows along the wall contains only air, evaporated fuel and very fine fuel droplets. This mixture is therefore very easy to ignite and can in fact be readily ignited by the ignition means or spark plug 2.

During the detonation, the mixture which is contained in the ante-chamber 2 is pushed back and in doing so it will partially traverse the apertured twin plate system 9 and 10 for the purpose of uninterruptedly conveying fuel. Flow in a backward direction through the conduit 4, of course, is prevented by the check valve (not shown). The back and forth movement of the combustion gases during the operation of the device has the effect that the heavier droplets which have moved further in a direction toward the combustion chamber are urged `backwardly and deposited at the walls of the ante-chamber 2. The ante-chamber walls are heated on the one hand by the radiation of the pulsating ame and on the other hand by the contact with the hot combustion gases but are also cooled by the cooling ribs 3. It is a simple matter to adjust the size and amount of cooling ribs such that the ordinary coking temperatures of the fuel, for example, diesel oil or heating oil will not be exceeded at least in the narrower portion of th-e ante-chamber. Instead of providing cooling ribs, other cooling means can -be used, for example, a cooling jacket could be provided or the heat might be dissipated by providing a strong heat exchanger or the like. A cooling jacket which could also be used in conjunction with the ribs which have been indicated in the drawing, could be connected to a combustion air supply 4 in such a manner that it can cause preheating of the combustion air.

It will be appreciated that in the present construction, the fuel jet enters first into the combustion chamber and only then is combustion air supplied through the opening 5. In this manner, a cooling fuel veil is placed in front of the discharge nozzle without providing an amount of oxygen which is necessary for combustion. In this manner, the free end of the nozzle is protected from high temperatures which prevail in a combustion chamber proper.

In this construction, the atomization is the same during the starting phase and also later onA In order to effect the atomization, the air or gas flow is employed which emanates from the space of the chamber 17 which is not filled with liquid fuel. The air supply 27 produces a super-atmospheric pressure in this space. This means that the fuel level in the collecting chamber is under pressure. The fuel is therefore positively conveyed or urged toward the atomizer nozzle and is thus not only conveyed yby the vacuum phase of the cycle. Therefore, in the inventive atomizer nozzle construction, an optimum atomization is effected.

The gas flow which fiows through the bore 25 has primarily a purpose of creating satisfactory atomization and only secondary the purpose of providing air for ignition. This is evident if one considers that the gases above the fuel level, that is for example gasoline vapors, contain only small quantities of oxygen. For this reason the air necessary for ignition should be provided before ignition in the combustion chamber and preferably through the conduit 4 and an opening 5 as indicated.

While a specific embodiment of the invention has been shown and described in detail to illustrate the application of the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A resonant burner comprising a tubular casing forming a combustion chamber with a resonant tube having an open end and an opposite end with an antechamber portion formed adjacent the opposite end having walls converging toward the opposite end, an atomizer means connected into said ante-chamber portion including a central conduit for directing a stream of starting air axially into the ante-chamber and combustion chamber and for permitting the oscillatable flow of combustion gases backwardly and forwardly therethrough, means for directing combustion air into said antechamber, and conduit means for supplying fuel radially of the central conduit for atomizing by said starting air stream and the combustion gases.

2. A resonant burner, according to claim 1, wherein said atomizer means includes in addition to said central conduit an outer pipe surrounding said central conduit defining an annular space for the flow of liquid fuel therethrough, and plate members closing said outer pipe and said central conduit, each plate member having an aperture therein for the axial flow of gases and fuel, the fuel flowing in the space between said plates in a radial direction from the annular space surrounding said central conduit into the gas and air stream for discharge into the combustion chamber.

3. A resonant burner, according to claim l, wherein said ante-chamber portion includes external cooling fins for maintaining this portion at a temperature at which coking of the fuel will not occur.

4. A resonant burner, according to claim 1, including means for directing combustion air tangentially into said combustion chamber adjacent said ante-chamber portion.

5. A resonant burner comprising an elongated tubular casing forming a combustion chamber having an opening at one end and having an ante-chamber portion which is closed at its opposite end, said ante-chamber portion being formed with walls diverging outwardly from the closed end toward said combustion chamber, a first pipe connected into the closed end of said combustion chamber having a plate with an aperture therein closing one end at a location adjacent the end of the ante-chamber portion of said combustion chamber, a fuel container connected to the opposite end of said first pipe at a location above the fuel level, a second pipe surrounding said first pipe and being slightly longer than said first pipe and defining an annular fuel passage between said first and second pipes, said fuel passage being connected to said fuel container below the level of fuel thereof for supplying fuel therethrough, said second pipe having a plate at its end adjacent the ante-chamber closed end with an aperture for the fiow of starting air and fuel therethrough, the space between the plate closing the end of said first pipe and plate closing the end of said second pipe defining a radial fuel flow chamber in which fuel is directed radially inwardly to the gas steam, and means for directing combustion air tangentially into said ante-chamber.

6. A resonant burner comprising an elongated tubular casing forming a combustion chamber having an opening at one end and having an ante-chamber portion which is closed at its opposite end, said ante-chamber portion being formed with walls diverging outwardly from the closed end toward said combustion chamber, a first pipe connected into the closed end of said combustion chamber having a plate with an aperture therein closing one end at a location adjacent the end of the ante-chamber portion of said combustion chamber, a fuel container connected to the opposite end of said first pipe at a location above the fuel level, a second pipe surrounding said first pipe and being slightly longer than said first pipe and defining an annular fuel passage between said first and second pipes, said fuel passage being connected to said fuel container below the level of fuel thereof for supplying fuel therethrough, said second pipe having a plate at its end adjacent the ante-chamber closed end with an aperture for the flow of starting air and fuel therethrough, the space between the plate closing the end of said first pipe and plate closing the end of said second pipe dening a radial fuel flow chamber in which fuel is directed radially inwardly to the gas stream, and means connected to said fuel container for supplying starting air under pressure at a location above theV fuel level for directing the starting air through said central pipe.

7. A resonant burner comprising an elongated tubular casing forming a combustion chamber having an opening at one end and having an ante-chamber portion which is closed at its opposite end, said ante-chamber portion being formed with Walls diverging outwardly from the closed end toward said combustion chamber, a first pipe connected into the closed end of said combustion chamber having a plate with an aperture therein closing one end at a location adjacent the end of the ante-chamber portion of said combustion chamber, a fuel container connected to the opposite end of said first pipe at a location above the fuel level, a second pipe surrounding said first pipe and being slightly longer than said first pipe and defining an annular fuel passage between said first and second pipes, said fuel passage being connected to said fuel container below the level of fuel thereof for supplying fuel therethrough, said second pipe having a plate at its end adjacent the ante-chamber closed end with an aperture for the flow of starting air and fuel therethrough, the space between the plate closing the end of said first pipe and plate closing the end of said second pipe delining a radial fuel flow chamber in which fuel is directed radially inwardly to the gas stream, said ante-chamber portion having cooling ns on the exterior thereof, and means for directing combustion air tangentially into the combustion chamber at the location of said ante-chamber portion.

References Cited by the Examiner UNITED STATES PATENTS 2,717,637 9/1955 Huber 15s- 4 2,814,930 12/1957 Meuiien et a1. 3,143,160 8/1964 Rydberg 15s-4 3,174,526 3/1965 von Linde 15s-4 3,189,017 6/1965 Hahn 158 4X FREDERICK L. MATTESON, IR., Primary Examiner.

ROBERT A. DUA, Examiner. 

1. A RESONANT BURNER COMPRISING A TUBULAR CASING FORMING A COMBUSTION CHAMBER WITH A RESONANT TUBE HAVING AN OPEN END AND AN OPPOSITE END WITH AN ANTECHAMBER PORTION FORMED ADJACENT THE OPPOSITE END HAVING WALLS CONVERGING TOWARD THE OPPOSITE END, AN ATOMIZER MEANS CONNECTED INTO SAID ANTE-CHAMBER PORTION INCLUDING A CENTRAL CONDUIT FOR DIRECTING A STREAM OF STARTING AIR AXIALLY INTO THE ANTE-CHAMBER AND COMBUSTION CHAMBER AND FOR PERMITTING THE OSCILLATABLE FLOW OF COMBUSTION GASES BACKWARDLY AND FORWARDLY THERETHROUGH, MEANS FOR DIRECTING COMBUSTION AIR INTO SAID ANTECHAMBER, AND CON- 